The present invention pertains generally to electromagnetic acoustic transducers, and more particularly to electromagnetic acoustic transducers of reduced thickness for use as buzzers in alarm electronic timepieces.
Electromagnetic acoustic transducers typically comprise a vibratory member supported at its periphery, and a drive system for electromagnetically driving the vibratory member into vibration to produce an audible sound. The drive system includes an excitation coil wound about a magnetic core and a set of permanent magnets all of which are mounted on a base plate. The two terminals of the coil extend through an opening in the base plate and are connected to electrodes formed on a lead substrate fixed to the underside of the base plate. A set of conductors connect the electrodes to circuitry for applying an alternating current drive signal to the excitation coil.
One drawback of the prior art construction is that it requires connection of the coil terminals to the electrodes on the underside of the lead substrate and such is a delicate and time-consuming manufacturing step. Another drawback is that the transducer requires sufficient space to accommodate the conductors which connect the electrodes on the underside of the lead substrate to the circuitry which applies the drive signal to the transducer thereby preventing a reduction in the thickness of the transducer. A further drawback is that no means are provided for accurately positioning the set of permanent magnets on the lead substrate so that the transducers exhibit different performance characteristics one from the other.